The present invention relates to piezoelectrical control elements. More, particularly, the present invention relates to a mirror transducer assembly for ring laser gyros.
Ring laser gyros require some form of path length control. Path length control in ring laser gyros has generally been provided by variety of piezoelectric element driven transducer assemblies. Such assemblies have included one or more piezoelectric elements. Examples of piezoelectric control elements used in ring laser gyro applications are illustrated in U.S. Pat. No. 3,581,227 issued to Podgorski, U.S. Pat. No. 4,383,763 issued to Hutchings et al., U.S. Pat. No. 4,697,323 issued to Ljung, et al., and U.S. Pat. No. 4,488,080 issued to Baumann.
Podgorski shows and claims the use of a transducer block, the block being composed of a dimensionally stable material as that used for the laser block which contains a lasing gas. The transducer block is circularly grooved on its internal side to leave a depressed thin integral gas impervious annular web or diaphragm extending between a central post and an outer rim, both being integral with the diaphragm. The central post is generally cylindrical and is inwardly-standing from and integral with the annular diaphragm. Radially outward from the groove is a rigid annular member or outer rim which is integral with the annular diaphragm but which extends axially external to the region enclosed by the annular diaphragm. Within an opening formed by the rigid annular member but external to the annular diaphragm is a stack of piezoelectric ceramic wafers which bear against the external side of the annular diaphragm and of the inwardly standing post. The opening containing the ceramic wafer stack is closed with a rigid disk-like member which is rigidly attached to the annular member to support the stack of ceramic wafers.
Further, on the external side of the central post is a light reflecting means, generally provided by a deposition of selected materials to form a mirror. The transducer assembly is positioned on the laser block to reflect the laser beams within the cavity provided by the laser block.
All of the, other aforementioned patents utilize one or more of the principles taught by Podgorski.
Ljung et al. and Hutching et al. teach the use of a double diaphragm mirror assembly which includes a piezoelectric driver assembly. The mirror assembly includes a central post which is coupled to a driver assembly. The driver assembly is a cup-shaped metallic driver fixture having a annular diaphragm extending between an integral central member and outer rim member. The central member is rigidly coupled to or attached to the central post of the mirror assembly. A pair of symmetrical donut-shaped piezoelectric disks are positioned on opposite sides of the annular diaphragm to provide the transducer action.
Ring laser gyros require that laser path length be maintained substantially constant. This is so since the laser beam intensity is dependent upon the path length. Variations in the beam intensity can adversely affect the performance parameters of the gyro, i.e., gyro errors. In order to maintain the ring laser path length constant, a mirror transducer like the ones already described are commonly employed.
The operating range of mirror transducers of the kind described is generally quite limited. Therefore, in ring laser gyro applications, commonly, a mode reset circuit is employed to always maintain the transducer within its operating limits. Herein mode is the equivalent of one wavelength of the laser beam. For a helium-neon laser, one mode is equal to 6328 Angstroms which is equal to 24.91 micro-inches. Temperature change of the gyro laser block as well as the transducer assembly, itself, are primary contributors to path length changes of the laser beam. Unfortunately, each "mode reset" of the transducer contributes to the overall gyro performance error budget.